CREATE TABLE t(indiv INT, grp STRING, val INT)
INSERT INTO t VALUES(1, 'A', 1)
INSERT INTO t VALUES(1, 'A', 2)
INSERT INTO t VALUES(1, 'A', 3)
INSERT INTO t VALUES(1, 'A', 4)
INSERT INTO t VALUES(2, 'A', 2)
INSERT INTO t VALUES(2, 'A', 2)
INSERT INTO t VALUES(2, 'A', 4)
INSERT INTO t VALUES(2, 'A', 8)
INSERT INTO t VALUES(3, 'B', 10)
INSERT INTO t VALUES(3, 'B', 20)
INSERT INTO t VALUES(3, 'B', 30)
INSERT INTO t VALUES(3, 'B', 40)
INSERT INTO t VALUES(4, 'B', 20)
INSERT INTO t VALUES(4, 'B', 20)
INSERT INTO t VALUES(4, 'B', 40)
INSERT INTO t VALUES(4, 'B', 80)


SELECT * FROM t 

FUNCTION myCov(x, y) {
  center_x := x - avg(x);
  center_y := y - avg(y);
  num := sum(center_x * center_y);
  denom := sqrt(sum(center_x * center_x)) * sqrt(sum(center_y * center_y));
  num / denom
  }


select myCov(1,2);